Installing A Hemi D.U.I Distributor - Fire That Hemi

Properly firing your engine's ignition is a necessity for good combustion-thus power. There are many aftermarket ignition choices for the RB Wedge and Hemi that offer added voltage to the spark plugs. Some long-time readers may recall we tested Performance Distributors (PD) 440 D.U.I. (Davis Unified Ignition) ignition back in our March '04 issue (Fire That Big Block). Nevertheless, that D.U.I. distributor is still under the hood of our 67 R/T test mule. Just a reminder, the 440 D.U.I. distributor only fits under the hood of non- Shaker, Air Grabber and Ram Charger equipped Mopars with stock type valve covers.

2/13It's no secret that Ray Barton Racing Engines has been building, dynoing, and shipping the latest version of the MP 528 Hemi crate engines. Before being crated, Barton dyno-tests all the engines using the same dyno distributor and ignition (MSD Pro Billet, Moroso Blue Max wires, MSD 7AL ignition box and MSD Pro Power coil). In this ignition shootout, Performance Distributors' (PD) new Hemi DUI distributor will have to prove itself without the help of the big MSD 7AL ignition box.

We were jolted to hear Performance Distributors has developed a Hemi D.U.I. distributor that clears the fat Hemi valve covers. One drawback-limited applications due to hood clearance. For Performance Distributors to offer a Hemi D.U.I. they needed to lengthen it 11/2-inches more than the 440 D.U.I. causing hood clearance issues. The benefits of the fatter/wider distributor are reduced spark scatter between the terminals, which leads to a smoother running engine. Inside the distributor is the Dyna-Module that adds dwell time for longer spark duration to ignite the combustion more completely. The coil, also inside the distributor cap, is a high voltage (50,000 volts) unit. All it takes is one 12-volt wire to power the D.U.I. ignition.

For a trial fit of the Hemi D.U.I., we used our '67 Coronet R/T. The tall distributor managed to fit under the hood when we used a stock type coil/cap cover (see captions 4, 5, and 6). It's most likely the Hemi D.U.I. won't fit under the hood of a Hemi A-Body unless the motor was in a lower than stock location.

3/13Baseline testing with the MSD ignition showed the Hemi was increasing power output on each pull. We installed the taller and wider D.U.I. distributor with only the 16-volt dyno wire to run the Hemi D.U.I. The stand-alone D.U.I backed up the MSD's numbers and power still increased on each pull as the Hemi continued breaking-in. The D.U.I. did well against a team of racing ignition components.

Fortunately, we were able to test the new Hemi D.U.I. using a brand-new Mopar Performance 528 Hemi crate engine at Ray Barton Racing Engines (all MP 528 Hemis are now built at Ray Barton Racing Engines). Before any MP Hemis are crated and shipped, they're dyno tested on Barton's DTS engine dyno for quality control. The 528 Hemi used for our ignition test was only the 17th Hemi crate engine that Barton's had built at that point. By the time you read this, RBRE will have built, dyno-tested, and shipped over a hundred MP 528 Hemis. Call any MP dealer to order your Hemi, not RBRE. Questions can be directed to the MP tech line: 888-528-HEMI.

The brand new 528 was run at 1,800 to 2,200 rpm for 25 minutes to properly break-in the flat tappet hydraulic cam and lifters. During that time, they monitor the oil pressure, water/oil temp, and check for any possible leaks. Afterwards, the valve settings are rechecked before any dyno pulls (usually three before crating) are made. Barton's dyno distributor is an MSD Pro Billet piece, using Moroso Blue Max ignition wires and an MSD 7AL ignition box. On its first pull the 528 made 642 hp at 6,200 rpm. By its fourth pull, power was up to 647 hp. We pulled out the MSD distributor, dropped in the D.U.I. and set the timing at the same 30 degrees full advance. The D.U.I. worked alone without the help of the big 7AL and MSD Pro Tower coil, using only one 16-volt wire to run. On its first pull the D.U.I. tied the MSD in power production and the Hemi marched on making more power as it continued breaking in. After three more pulls the 610 hp (rated) Hemi was putting out 650 hp at 6,200 rpm! The Barton's (Ray and son Dave) commented that these new Hemis need over 20 pulls before power stops climbing. Dave reinstalled the MSD ignition to demonstrate, and the Hemi backed-up the 650 hp. This only verified the MSD Pro Billet/7AL vs. the D.U.I. was a dead-heat ignition duel. It was senseless for us to make any more pulls (these crate Hemis usually get 3-4 pulls); we'll let the lucky new Hemi-owner enjoy breaking it in.

4/13Here Dave Barton sets the D.U.I's timing at the same 30-degrees for a fair comparison. When you consider the mild build-nature of the Crate Hemi (.540-inch lift cam, 10.5:1 compression, un-ported heads/intake, and an 830cfm Holley HP with no special tuning), these Hemi's produce amazing power (over 650).

Since the 440 D.U.I. will not fit a Wedge engine with Indy heads, we felt that maybe the Hemi D.U.I. would be tall enough to fit one. Good friend Vic Palombo graciously lent us his '66 Charger with an Indy-headed RB, and our buddies at SLP welcomed the Charger for a flogging on their chassis dyno. This time the Hemi D.U.I. would be up against the MSD Pro Billet distributor with a more street-like MSD 6AL ignition box and MSD Blaster coil. For our baseline pull, the rwhp was 457 at 6,200 rpm, and the air/fuel (A/F) mixture ratio was a good-looking 12.8 at WOT (wide open throttle). Timing was at 39 degrees total-right where this Indy-headed Wedge makes its most power. We made three more pulls to confirm there was consistent power production.

8/13Further competition for the Hemi D.U.I. would be your typical street type ignition. Vic Palumbo's '66 Charger features a Indy-headed 493-inch Wedge, and the ignition is an MSD Pro Billet distributor and a 6AL box and Blaster coil, with 8.5mm Super Conductor plug wires. We baseline tested the MSD ignition on SLP's SuperFlow SF840 chassis dyno.

At Vic's home garage, all the MSD ignition components and wiring were removed. This really cleaned up the engine compartment (see pics). We used the stock 12-volt wire that originally juiced the positive side of the coil to power the D.U.I. distributor. The original ballast resistor was bypassed. With the Hemi D.U.I. dropped in place, the stroked Wedge fired right up. We immediately noticed that it was running smoother and with better throttle response.

Now back at SLP, we made certain the timing was set at the same 39 degrees. With the Charger securely strapped down, the moment of truth came when SLP's Hank Denieki (Chief Engineer) punched the pedal down. We were very pleased to learn we picked up 5 rwhp. With the A/F at the same 12.8 we didn't need to reach into our boxes of Holley tuning supplies. Again, we made three more pulls to check consistency.

9/13The fender well area gained a cleaner appearance without the MSD ignition box, coil, and wiring. The DUI distributor made its presence known-it's big, tall and intimidating. We set the timing at the same 39-degrees total, and the Wedge idled noticeably smoother and the throttle response felt better. Ditto for our road test.

As an added bonus to our testing of the Hemi D.U.I., we wanted to see if Performance Distributors' Mini VIP (18-volt step-up regulator) would step up the power. The Mini VIP was plugged into the D.U.I. and another spin of the roller showed us 5 more horsepower to the wheels. That's enough of a power increase to be worth a tenth at the track. The additional spark output changed the combustion burn to a lean and mean 13.0 A/F. This was on an exceptionally warm and humid December day (72 degrees, 77 percent humidity). If it was cool and dry we would have richened it up for a few more hp but we left well enough alone.

ConclusionTesting ignitions and seeing and hearing the new Street Hemi make 650 hp was amazing, considering we did no special tuning (using only an 830 Holley HP with 30 degrees timing, and unported heads and intake) on the mild-mill. Most enthusiasts with a Hemi or Indy-headed Wedge will see more power using the Hemi D.U.I.-if it will fit under the hood!